The present invention relates to a device for controlling a windshield wiper, in particular on a motor vehicle.
Devices for controlling windshield wipers are known in which the windshield-wiper motor starts up automatically when a predetermined threshold for the wetting of the windshield by rain is exceeded. Various sensors are known in order to recognize the wetting of the windshield. Furthermore in the known devices the threshold value is predetermined as a fixed value or as variable in steps.
The specific sensor used however supplies, in cooperation together with a threshold value circuit, a signal which does not sufficiently reflect the extent to which visibility is impaired at the time. This impairment depends on many, in part, subjective factors. Thus, for instance, the individual visual acuity and the other viewing conditions play a decisive role. Raindrops have a much more disturbing effect at night than during the day, due to dazzle by oncoming vehicles. Vision is furthermore affected to varying extents by the size of the raindrops, by the surface tension and by the degree of the dirtiness of the windshield. Finally, sensor-induced changes reduce the importance of the sensor signal as measurement of the visibility. Such changes comprise, for instance, temperature dependence and aging processes, manufacturing tolerances and the conductivity of the rain in the case of capacitive and resistive sensor systems.